Hot Tear Susceptibility of Al-Mg-Si-Fe Alloys with Varying Iron Contents
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HOT tearing is a defect that can be observed in many casting processes, from direct chill casting of primary alloys to shape casting of recycled alloys. It is particularly harmful because it can manifest as cracks that can cause failure in further processing operations of wrought alloys or cause lack of pressure tightness or premature failure of shape castings. If hot tears are observed at the point of casting, it means the casting must be scrapped. In direct chill casting of aluminum alloys, hot tearing is one of the major defects observed, which is one reason why there is considerable literature[1–4] devoted to understanding the mechanisms of hot tearing. Hot tearing is complex because of many factors that can influence it.[1] A key factor is the buildup of shrinkage strain during solidification; hence, understanding the strain and stress development in a casting during solidification is of utmost importance.[5–7] Therefore, there is a substantial contribution in the literature related to modeling the phenomena related to hot tearing,[2,7,8] particularly in direct chill casting processes. LISA SWEET, Senior Research Engineer, CAST MARK A. EASTON, CEO, CAST, and MALCOLM J. COUPER, Adjunct Professor, are with the Department of Materials Engineering, Monash University, Clayton, Melbourne, VIC 3800, Australia. Contact e-mail: [email protected] JOHN A. TAYLOR, Associate Professor, CAST, is with the School of Mechanical and Mining Engineering, The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia. JOHN F. GRANDFIELD, Director, is with the Grandfield Technology Pty. Ltd., Brunswick, VIC 3055, Australia. CAMERON J. DAVIDSON and LIMING LU, CAST, Research Scientists, CSIRO, are with the Division of Process Science and Engineering, Pullenvale, Queensland 4069, Australia. DAVID H. STJOHN, Director, Centre for Advanced Materials Processing and Manufacturing (AMPAM), The University of Queensland, St Lucia, Brisbane, QLD 4072, Australia, and is also with the School of Mechanical and Mining Egineering, The University of Queensland. Manuscript submitted August 9, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS A
While modeling has been relatively successful in predicting hot tearing, it has mostly been applied to simple alloy compositions such as binary alloys[9–13] or has only considered processing variations on a particular alloy composition.[14,15] Studies of this type have proved very enlightening. It is well known that most binary alloys display a lambda curve behavior[11,16,17] where, as the alloy concentration increases, the hot tearing susceptibility increases and then decreases again, and this correlates reasonably well to the non-equilibrium solidification range of an alloy. Similar behavior has also been observed in ternary alloys including Al-Mg-Si alloys[18] which are the focus of study in this article. Impurity elements have also been observed to affect hot tear susceptibility.[19–21] Hot tearing has been studied both by observation and measurement and through the development of models to explain
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